The invention relates to a process for the operation of a bobbin creel for a winding system. With such a process, the best possible tension compensation of all the threads on a bobbin creel is striven for, because the different running lengths of the threads between the winding heads and the winding machine and the thread guide connected to them can, without the appropriate tension compensation may lead to different thread tension values. The consequence of this would be an unequal winding density.
From EP-A 319 477 a device is known for the tension compensation of the threads on a bobbin creel, with which, by means of a common control rod, the thread brakes (yarn tensioning devices) of the vertical rows of winding heads can be subjected to different force values. The control rod is activated by drive motors, which receive actuating signals from a processor. In this situation, the actual value of the thread tension of a whole thread bundle is measured by means of a measurement roller shortly before winding. It is not possible in this situation to take account of the thread tension of individual threads or individual groups of threads.
DE-A 195 46 473 discloses a process for the control of winding devices for yarn sheets. In this case too, measurement of the tension of the thread bundle is effected shortly before winding, in order to exert an effect on the tension of the threads on the bobbin creel by way of means which are not represented in any greater detail. With the aid of a measurement carriage which is capable of being moved transversely over the thread bundle, however, the sequential tension measurement of individual threads at a predetermined time interval is possible. From this a mean tension value is formed, in accordance with which the common tension of all the threads is effected. With this process, an individual control of individual threads or individually groups of threads can hardly be achieved, because it is not possible to scan each thread simultaneously. Further disadvantages of this process are that measurement at intervals is too slow with the winding speeds used today and, in addition, the thread being measured in each case is subjected to mechanical stress by the measuring means, which has the effect of changing the individual tension of a thread.
DE-A 44 18 729 likewise relates to a device for controlling the thread tension on a bobbin creel. This device features a brake rotor for each bobbin creel directly at the winding head. A tension lever serves as the measurement sensor for the thread tension, said lever being imposed by the wound-up thread. At each bobbin holder a load-imposing device operating with fluid pressure engages on the tension lever, whereby the fluid pressure is adjustable in common for all load-imposition devices. The individual control of the thread tension can therefore be overlaid by a general adjustment capability for all thread tensioners. One disadvantage of this arrangement lies in the fact, however, that the control circuit is restricted directly to the winding head. This arrangement is not well-suited for a bobbin creel with an overhead withdrawal. In addition, braking directly at the bobbin holder is not well-suited for all work processes, and the different running lengths of the threads between the winding head and the winding machine are not taken into account.
Finally, DE-U-296 08 169 discloses a winding device for threads of bobbin creels with which a measurement device is arranged for the determination of thread tension in threads, whereby the central adjustment of preliminary twisting rails allocated to the winding heads can be controlled in accordance with the measurement result. The measuring device consists of individual pressure measuring strips, which in each case support a plurality of threads. Accordingly, monitoring of the tension in individual threads is likewise not possible, apart from the fact that the pressure measurement strips in each case can only be imposed on the outermost threads of a thread bundle.
The problem of the invention is therefore of creating a process of the type described above, which by simple means will allow for the optimum and versatile application of control of the overall winding process. In this situation, it is also intended that modern electronic means should be capable of being used, with low energy consumption. The creel control should be capable of adaptation to as many different operational conditions as possible. This problem is resolved according to the invention by a process described below.
By means of the sustained measurement of the actual value of the thread tension on each thread, the tension behavior of the threads on the entire creel can be acquired with minimal time delay. Measurement is effected in this situation in the area between leaving the creel and winding up on the winding machine, by means of which it can be assured that the different running lengths and deflections of the threads is taken into account. The control process can be designed individually for single threads or for groups of threads, as a result of which the creel can be put to versatile use. The mechanical function and arrangement of the thread brakes plays only a subordinate role in this situation. By means of this process, thread influences can be compensated for, such as different thread thicknesses, thread structure, other material influences and influences at the unwinding point in the bobbin creel.
Of particular advantage with the process according to the invention is the fact that each individual thread brake can be activated with a drive motor allocated to it. This is possible without further ado with the economically-priced miniaturized drive units available today.
It is also possible with the process according to the invention, however, for the thread brakes of each thread group with the same running length to be activated by a drive motor. As a rule, the threads from vertical rows (rails) of winding heads per bobbin side form in each case a thread group with the same running length. It is therefore possible, in an inherently known manner, for all thread brakes on a vertical row (rail) to be activated by a common drive element, whereby the drive motor is arranged in the area of the uppermost or lowest winding head. Accordingly, it is also possible for a group control to be carried out for a desired thread group, with one drive motor in each case.
In certain cases it is sufficient if the actual value is measure on at least two threads from each thread group with the same running length, and if, from the minimum of two actual values, a mean actual value is formed, which is compared with the specified value. This measuring principle is based on the assumption that the threads of a specific thread group behave in approximately the same manner. Despite the selective measurement, however, the application of the thread brakes both by means of individual drive motors on each thread brake as well as by means of a common drive motor is possible.
Further advantages according to the invention can be obtained if the threads are subjected to an additional brake force in the thread run direction before each thread brake at at least one preliminary tension device, which is set as a basic value or which is adjusted as a function of the measured actual value.
Depending on the material properties, such as quality, twist, strength, and heel inclination etc. of the threads, different preliminary tension devices must be used in order to guarantee trouble-free withdrawal of the threads. Preliminary tensioning devices on a twist basis, such as eyelet pretensioners, crepe pretensioners, etc., can be adjusted individually or rail by rail by a drive motor, in order to obtain optimum thread withdrawal.
It is also possible for the different running lengths of the threads or thread groups (creel length compensation) to be compensated for exclusively with the aid of the preliminary tension devices. In this way the downstream thread brakes will be relieved of this mandatorily required compensation task, and they can then develop their full degree of efficiency with regard to their braking force.
In addition to this, preliminary tensioning devices of the type referred to heretofore can also be used to increase the thread tension before the intake into the thread brakes, whereby the thread tension can be adjusted in common with the thread brake individually or group by group. These preliminary tensioning devices can also be used as individual means for the distribution of the tension, however. In this situation, no additional thread brakes are required, which is economically very favorable. The expression xe2x80x9cthread brakesxe2x80x9d as used here accordingly also encompasses all preliminary tensioning devices in the broadest sense.
In specific cases it is of advantage if, at the winding machine, the tensile force of the entire entity of the threads, combined into a yarn strip, is measured in the area in front of the winding take-up point as a strip actual value, and is compared with a strip specified value, and if, in the event of a deviation being detected, all the thread brakes are adjusted in such a way that the strip tension actual value approximates the strip specified value. This additional control of the strip tension predominates over the control of the thread tension described heretofore, whereby all changes in tension between the thread tension sensors and the winding take-up point will be taken into account.
The invention also relates to a bobbin creel for a winding system. With a bobbin creel of this nature, the thread tension is measured individually on each thread by means of thread tension sensors.
The use of at least two thread tension sensors is also conceivable, however, for the measurement of at least two threads from each group of threads of the same running length, in order to form a mean value from this.
The measurement is effected to advantage in this situation on threads which are not withdrawn from adjacent winding heads of the corresponding rails.
There are a number of fundamentally different principles of thread tension sensors known. Sensors have proved to be of particular advantage for the purpose accordingly to the invention, however, which feature a force measuring device with a measuring element imposed transversely to the thread. A thread tension sensor of this type is described, for example, in DE-A 197 16 134, the disclosure content of which is hereby adopted in full. The sensor is of compact design, with small external dimensions, and is relatively insensitive to dirt contamination. The measuring bridge, which operates on a piezo-resistive basis, requires very little energy, which plays a not inconsiderable role with the possibly large number of sensors. The measurement is also effected in directly linear fashion with the movement of the measurement sensor, as a result of which the possibility of measurement error is reduced.
The thread tension sensor can also be functionally employed in a particularly simple manner as a thread monitor for monitoring thread run or thread breakage. In the event of the thread tension of one or more threads exceeding or falling short of the lower or upper control range respectively, a warning signal is issued, or the winding system can be stopped automatically.
The functions of the thread tension sensor described can also be used, in addition to controlling the thread tension, as a monitoring function in a winding system for the entire yarn sheet.
To particular advantage, stepping motors are used as the drive motors for the thread brakes (normal pressure thread brake, such as disk brakes, twist thread brakes, dynamic thread brakes, etc.) or for the preliminary tensioning devices referred to (eyelet preliminary tensioning device, crepe preliminary tensioning device), which take effect on the braking media by means of a self-retaining gear system. The advantage of these stepping motors lies in the fact that they consume energy only during activation, but not during the stopping phase. This accordingly allows for the energy consumption to be substantially reduced. A self-locking drive motor, for example with a worm drive or a self-locking spindle drive, allows for a position to be retained which the stepping motor has moved into. The advantage of the stepping motor also lies in the fact that each time the positions of the thread brakes or the positions of the preliminary tensioning devices are known and can be calibrated.
At least one signal component can be allocated to each winding head, in particular a thread monitor for monitoring the thread run or thread break, and/or a visual signaling medium for identifying the winding heads or as a plug-on aid. Thread monitoring can be carried out in accordance with various different and inherently-known function principles, such as, for example, the mechanical drop needle principle, Hall sensors, optical monitoring devices, etc. A signal medium for facilitating the equipping of a bobbin creel is known, for example, from EP-A-329 614.
All electrically-actuatable means allocated to a winding head, in particular the drive motors for the thread brakes, but also the signal components referred to, can be activated via common signal lines. For this purpose, they are in functional connection with a central control device via serial interfaces. This evidently makes it possible for elaborate wiring of the individual components to be done away with.